These are Birmingham view and proof marks, showing that this Colt revolver was exported to Britain and used in their army; the point-to-point "broad arrows" on the sideplate and crane show that this revolver was then sold out of service, almost certainly to the officer that carried it as his service revolver. The British ordered these revolvers in their standard service cartridge of the time, 455 Eley revolver, which is hard to get and fairly expensive today, and you shouldn't try to fire anything else in it; most of the people who own a revolver in this calibre today will reload it themselves. Someone with the proper reference books on Colts can probably tell you exactly when this revolver was originally sold. HTH.
Gun control in Canada: making the streets safer for rapists, muggers, and other violent criminals since 1936.